The present invention relates to an image reading apparatus for obtaining a digital image having gradation of binary-level or multilevel in a computer, a word processor, a digital copying machine or the like.
In an exemplary image reading apparatus used in a computer or the like, as shown in FIG. 14, an original 203 is placed on the upper side of a housing 201 which includes a platen glass (not shown) at the upper surface thereof, so as to read an image from the original 203. A reduction optical system, disposing the housing 201 includes a light source 205, mirrors 207, a lens 209, and a solid-state imaging device (for example, a CCD) 211.
Another type of image reading apparatus, as shown in FIG. 15, includes a light source 205A, a rod lens array 213, and a contact-type sensor 215 which constitute an isometric optical system. These optical elements are disposed in a housing 201A which includes a platen glass (not shown) at the upper surface thereof. A light emitted from the light source 205 or 205A is reflected from the original 203 or 203A. The reflected light is incident on the solid-state imaging device 211 or the contact-type sensor 215 through the reduction or isometric optical system so as to form an image. Then, the reflected light corresponding to the density of the original is converted into an electric signal.
According to each of the above conventional configurations, it is necessary to provide the platen glass for placing the original 203 or 203A thereon, so that the width and depth of the apparatus are required to be larger than those of the original 203 or 203A. Regarding the height of the image reading apparatus, a height of about 10 to 30 cm is required to contain the reduction or isometric optical system. Therefore, a problem exists in that the size of the image reading apparatus is large.
Since the conventional image reading apparatus is relatively large, it cannot be utilized for inputting an image into a personal computer, a word processor, or the like which is located on a desk for personal use. Thus, it is greatly desirable to miniaturize an image reading apparatus.
An image reading apparatus 100 of desktop type which can obtain an image with desired resolution can be realized as shown in FIG. 13, by providing a scan mechanism unit 1 having optical means, capable of forming an image with variable magnification, and a solid-state imaging device which is disposed so as to have a predetermined positional relationship with respect to the optical image forming means.
The image reading apparatus 100 is constructed in such a manner that the scan mechanism unit 1 is fixed at the upper end of a support column 102 which stands on a flat plate 101, so that an imaging device therein can read an original 103 placed on a desk or other flat surface. In the image reading apparatus 100, the distance between the original 103 and the imaging device is larger than that in a conventional image reading apparatus. Accordingly, the image reading apparatus 100 has a problem in that, although the imaging device is fixed, the image thus read can be shifted to a large extent from the intended reading position by a slight directional deviation of the imaging device.
Therefore, the mechanical system which controls the imaging direction and the position of the image reading apparatus is required to operate with high positional accuracy. This limits the miniaturization of the scan mechanism unit 1 and hence it is difficult to miniaturize the image reading apparatus.